title: Neuropeptide Y-deficient mice show altered circadian response to simulated natural photoperiod.
abstract: Circadian rhythms, endogenously generated by the suprachiasmatic nucleus (SCN), can be synchronized to a variety of photic and non-photic environmental stimuli. Neuropeptide Y (NPY) is produced in the intergeniculate leaflet (IGL) and known to mediate both photic and non-photic influences on the SCN. We recently found that npy-/- mice were slower to shift their locomotor activity onset to the new time of light offset when photoperiod was abruptly changed from light/dark (LD) cycle 18:6 to LD 6:18. In the present study, we measured the locomotor response of npy-/- mice to gradual changes in photoperiod (4 min a day) for 141 days (LD 16:8 changing to LD 8:16), mimicking external LD cycles in nature. When the photoperiod approached LD 8:16, npy-/- mice showed a significantly delayed onset of activity compared to wild-type mice. Activity patterns disintegrated into multiple bouts and intensity of activity decreased as the photoperiod changed and these changes were more pronounced in npy-/- mice. Our results lend further support to the idea that NPY is involved in circadian entrainment responses to seasonal photoperiod changes.
authors.affiliation: Neuroscience Program, Smith College, Northampton, MA 01063, USA.
authors.forename: Hyun Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Mary E
authors.initials: ME
authors.lastname: Harrington
mesh_terms: D000204:Activity Cycles / Q000235:genetics; D000222:Adaptation, Physiological / Q000235:genetics; D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009043:Motor Activity / Q000235:genetics; D009478:Neuropeptide Y / Q000235:genetics / Q000378:metabolism*; D017440:Photoperiod; D012621:Seasons
chemical_list: D009478:Neuropeptide Y